The present invention is applicable to the field of lubricants, and more particularly to the field of lubricants for marine engines, in particular for two-stroke marine engines. More particularly, the present invention relates to a lubricant for marine engines comprising at least one base oil, at least one overbased detergent, at least one neutral detergent and at least one fatty amine. The lubricant according to the invention can be used both with fuel oils with a high sulphur content and fuel oils with a low sulphur content. The lubricant according to the invention has sufficient neutralizing power vis-à-vis sulphuric acid formed during the combustion of fuel oils with a high sulphur content, while limiting the formation of deposits during the use of fuel oils with a low sulphur content.
The lubricant according to the invention more particularly makes it possible to prevent corrosion and/or reduce the formation of insoluble metallic salt deposits in two-stroke marine engines during the combustion of any type of fuel oils, i.e. with a high and with a low sulphur content. The lubricant according to the invention also has good properties of thermal resistance and cleanliness of the piston-cylinder assembly. The present invention also relates to a method for lubricating a marine engine, and more particularly a two-stroke marine engine that can be used both with fuel oils with a high sulphur content and fuel oils with a low sulphur content utilizing this lubricant. The present invention also relates to a composition of the additive-concentrate type comprising at least one fatty amine.
The marine oils used in slow-speed two-stroke crosshead engines are of two types: cylinder oils on the one hand, ensuring the lubrication of the piston-cylinder assembly, and system oils on the other hand, ensuring the lubrication of all the moving parts other than those of the piston-cylinder assembly. Within the piston-cylinder assembly, the combustion residues containing acid gases are in contact with the lubricant oil. The acid gases are formed during the combustion of the fuel oils; these are in particular sulphur oxides (SO2, SO3), which are then hydrolysed during contact with the humidity present in the combustion gases and/or in the oil. This hydrolysis generates sulphurous acid (HSO3) or sulphuric acid (H2SO4).
In order to preserve the surface of the liners and prevent excessive corrosive wear, these acids have to be neutralized, which is generally carried out by reaction with the basic sites included in the lubricant. The neutralizing capacity of an oil is measured by its BN or Base Number, which characterizes its basicity. It is measured according to the standard ASTM D-2896 and is expressed in equivalents by weight of potash per gram of oil or mg of KOH/g of oil. The BN is a standard criterion making it possible to adjust the basicity of the cylinder oils to the sulphur content of the fuel oil used, in order to be able to neutralize all of the sulphur contained in the fuel, and capable of being converted to sulphuric acid by combustion and hydrolysis.
Thus, the higher the sulphur content of a fuel oil, the higher the BN of a marine oil must be. This is why marine oils with BNs varying from 5 to 100 mg KOH/g of oil are available on the market. This basicity is provided by detergents which are overbased with insoluble metallic salts, in particular metallic carbonates. The detergents, mainly of the anionic type, are for example metallic soaps of the salicylate, phenate, sulphonate, carboxylate type, etc. which form micelles where the insoluble metallic salt particles are maintained in suspension. The usual overbased detergents intrinsically have a BN conventionally comprised between 150 and 700 mg of potash per gram of detergent. Their content by mass in the lubricant is determined as a function of the level of BN to be achieved.
A part of the BN can also be provided by non-overbased or “neutral” detergents with a BN typically less than 150 mg of potash per gram of detergent. However, it is not possible to envisage producing cylinder lubricant formulas for marine engines, in particular for two-stroke marine engines, where the entire BN is provided by “neutral” detergents: it would in fact be necessary to incorporate them in excessive quantities, which could be detrimental to the efficiency of the lubricant and would not be realistic from an economic point of view.
The insoluble metallic salts of the overbased detergents, for example calcium carbonate, therefore contribute significantly to the BN of the usual lubricants. It can be considered that approximately at least 50%, typically 75%, of the BN of the cylinder lubricants is thus provided by these insoluble salts. The actual detergent part, or metallic soaps, found in both the neutral and overbased detergents, typically provides most of the remainder of the BN.
Environmental concerns have led, in certain areas and in particular coastal areas, to requirements relating to the limitation of the levels of sulphur in the fuel oils used on ships. Thus, the MARPOL Annex 6 regulations (Regulations for the Prevention of Air Pollution from Ships) issued by the IMO (International Maritime Organization) entered into force in May 2005. It sets a maximum sulphur content of 4.5% by weight with respect to the total weight of the fuel oil for heavy fuel oils as well as creating sulphur oxide emission control areas, called SECAs (SOx Emission Control Areas). By heavy fuel oils is meant high-viscosity fuels mainly used for large diesel engines installed on board ships. Thus, ships entering these areas must use fuel oils with a maximum sulphur content of 1.5% by weight with respect to the total weight of the fuel oil or any other alternative treatment aimed at limiting SOx emissions in order to comply with the specified values.
More recently, amendments have been made to the MARPOL Annexe 6 Regulations. These amendments are summarized in the table below. Thus, the restrictions on the maximum sulphur content have become more severe with a worldwide maximum content reduced from 4.5% by weight with respect to the total weight of the fuel oil to 3.5% by weight with respect to the total weight of the fuel oil. The SECAs (Sulphur Emission Control Areas) have become ECAs (Emission Control Areas) with an additional reduction in the maximum permissible sulphur content from 1.5% by weight with respect to the total weight of the fuel oil to 1.0% by weight with respect to the total weight of the fuel oil and the addition of new limits relating to contents of NOx and particles.
Amendments to MARPOL Annex 6(MEPC Meeting No. 57 - April 2008)General limitLimit for the ECAsMaximum3.5% by weight with1% by weight with respectsulphur contentrespect to the totalthe total weight of theweight of the fuel oil onfuel oil on Jan. 7, 2010Jan. 1, 20120.5% by weight with0.1% by weight withrespect to the totalrespect to the total weightweight of the fuel oil onof the fuel oil onJan. 1, 2020Jan. 1, 2015
Ships sailing trans-continental routes use several types of heavy fuel oil depending on local environmental constraints whilst making it possible for them to optimize their operating costs. This situation will continue whatever the final level of the maximum sulphur content permissible in fuel oils. Thus many container ships are utilizing several bunker tanks, for a fuel oil with a high sulphur content (at most 3.5% by weight of sulphur with respect to the total weight of the fuel oil and above) or “high seas” fuel oil on the one hand, and for an “ECA” fuel oil with a sulphur content of less than or equal to 1% by weight with respect to the total weight of the fuel oil on the other hand.
Changing between these two categories of fuel oil can require adaptation of the engine's operating conditions, in particular the utilization of appropriate cylinder lubricants. At present, in the presence of fuel oil with a high sulphur content (3% by weight with respect to the total weight of the fuel oil and above), marine lubricants having a BN of the order of 70 mg of KOH/mg of lubricant are mainly used. In the presence of a fuel oil with a low sulphur content (1% by weight with respect to the total weight of the fuel oil and below), marine lubricants having a BN of the order of 40 mg of KOH/mg of lubricant are mainly recommended. In both these cases, a sufficient neutralizing capacity is then achieved as the necessary concentration at basic sites provided by the overbased detergents of the marine lubricant is reached, but it is necessary to change lubricant each time the type of fuel oil is changed.
Furthermore, each of these lubricants has limits of use for the following reasons: the use of a cylinder lubricant with a BN of 70 mg of KOH/g of lubricant in the presence of a fuel oil with a low sulphur content (1% by weight with respect to the total weight of the fuel oil and below) and a fixed level of lubrication, creates a significant excess of basic sites and a risk of destabilization of the unused overbased detergent micelles, which contain insoluble metallic salts. This destabilization results in the formation of deposits of insoluble metallic salts (for example calcium carbonate) having a high degree of hardness, mainly on the piston crown, and can in the long term lead to a risk of excessive wear of a piston-liner polishing type. As for the use of a cylinder lubricant of BN 40 mg of KOH/g of lubricant, such a BN does not provide the lubricant with sufficient neutralizing capacity and can thus lead to a significant risk of corrosion.
Thus, the optimization of the cylinder lubrication of a two-stroke engine then requires the selection of a lubricant the BN of which is suited to the sulphur content of the fuel oil used and to the engine's operating conditions. This optimization reduces the flexibility of operation of the engine and requires significant technical skill on the part of the crew in defining the conditions under which the change from one type of lubricant to the other must be carried out.
In order to simplify operations, it would therefore be desirable to have a single cylinder lubricant, in particular for two-stroke marine engines, that can be used both with high-sulphur fuel oils and with low-sulphur fuel oils. In particular, a need exists for formulations in which the BN is provided in an alternative way to the overbased detergents, by compounds that do not give rise to metallic deposits when they are present in excess relative to the quantity of sulphuric acid to be neutralized. Several solutions have been proposed in order to meet this need.
Document WO 2009/153453 describes a cylinder lubricant for two-stroke marine engines that can be used both with fuel oils with a high sulphur content and fuel oils with a low sulphur content and comprising at least one overbased detergent and at least one oil-soluble fatty amine. However, in this lubricant, the presence of a neutral detergent is optional. Furthermore, in this lubricant, the percentage by mass of overbased detergents with respect to the total weight of the lubricant is selected so that the BN provided by the metallic carbonate salts represents a contribution of at most 20 milligrams of potash per gram of lubricant to the total BN of the lubricant. Moreover, the fatty amines exemplified in this document and making it possible to improve the neutralization efficiency correspond to fatty mono- or di-amines.
Document WO 2012/140215 describes a cylinder lubricant for two-stroke marine engines that can be used both with fuel oils with a high sulphur content and fuel oils with a low sulphur content and comprising at least one overbased detergent, at least one neutral detergent and at least one alkoxylated fatty amine. However, the alkoxylated fatty amines exemplified in this document and making it possible to improve the neutralization efficiency correspond to alkoxylated fatty monoamines. Moreover, the BN of the lubricant described in this document cannot be too high, and in particular cannot be greater than 55 mg of KOH/mg of lubricant.
In addition to the constraints of neutralization efficiency vis-à-vis fuel oils with a high sulphur content and with a low sulphur content, increased thermal resistance requirements for the lubricant, and therefore cleanliness of the ring-piston-cylinder zone (or RPC zone) are to be taken into account. It would thus be desirable to have available a cylinder lubricant for marine engines, in particular for two-stroke marine engines, that can be used both with fuel oils with a high sulphur content and fuel oils with a low sulphur content and making it possible to have both a high BN, in particular of at least 50 mg KOH/g of cylinder lubricant, and a good neutralizing capacity, while having good thermal resistance and thus good cleanliness of the engine, and in particular of the piston-cylinder assembly. It would also be desirable to have available a cylinder lubricant for marine engines, in particular for two-stroke marine engines, presenting little or no risk of thickening over time, and in particular during use.
An objective of the present invention is to provide a cylinder lubricant overcoming some or all of the abovementioned drawbacks. Another objective of the present invention is to provide a cylinder lubricant that is resistant to ageing and retains its properties over time. Another objective of the invention is to provide a cylinder lubricant the formulation of which is easy to implement. Another objective of the present invention is to provide a method for lubricating a marine engine, and more particularly a two-stroke marine engine that can be used both with fuel oils with a high sulphur content and fuel oils with a low sulphur content.
The present invention relates to a cylinder lubricant having a BN that is sufficiently high to efficiently neutralize sulphuric acid formed during the use of fuel oils with a high sulphur content, a significant part of said BN being provided by oil-soluble species which do not give rise to metallic deposits when they are partially consumed during the use of fuel oils with a low sulphur content.
The present invention therefore relates to a cylinder lubricant having a BN determined according to the standard ASTM D-2896 greater than or equal to 50 milligrams of potash per gram of lubricant, comprising:                at least one lubricant base oil,        at least one detergent based on alkali or alkaline-earth metals, overbased with metallic carbonate salts,        at least one neutral detergent,        a mixture of fatty amines comprising at least one fatty amine of formula (I):R1—[NR2(CH2)3]3—NH2   (I)        in which:                    R1 represents a linear or branched, saturated or unsaturated alkyl group, comprising at least 14 carbon atoms,            R2 represents a hydrogen atom or a —(CH2)2OH group,                        the content by weight of fatty amine of formula (I) being greater than or equal to 90% with respect to the total weight of the mixture of fatty amines, the fatty amine having a BN determined according to the standard ASTM D-2896 ranging from 150 to 600 milligrams of potash per gram of amine, the percentage by mass of fatty amine with respect to the total weight of the lubricant being selected so that the BN provided by this compound represents a contribution of at least 10 milligrams of potash per gram of lubricant to the total BN of said cylinder lubricant and, the percentage by mass of the overbased detergent with respect to the total weight of the lubricant being selected so that the BN provided by the metallic carbonate salts represents a contribution of at least 20 milligrams of potash per gram of lubricant to the total BN of said cylinder lubricant.        
The applicant has found that it was possible to formulate cylinder lubricants where a significant part of the BN is provided by fatty amines that are soluble in the lubricant base oil, while maintaining the level of performance with respect to standard formulations with an equivalent or even greater BN. The performances in question here are in particular the capacity to neutralize sulphuric acid, measured using the enthalpy test described hereafter, as well as thermal resistance, measured using the ECBT test also described hereafter. The cylinder lubricant according to the invention thus has such performances, while retaining a viscosity which makes it suitable for its use.
However it is not possible to completely dispense with the provision of BN by the insoluble metallic particles of the overbased detergents: in fact they constitute the “ultimate reserve” of basicity that is indispensable when operating with fuel oils with a high sulphur content, for example greater than 3% by weight with respect to the total weight of the fuel oil. These insoluble metallic salts also have a favourable anti-wear effect as long as they are maintained dispersed in the lubricant in the form of stable micelles. The applicant has also surprisingly found that in the presence of a significant provision of BN by said fatty amines, and despite a significant provision, i.e. of at least 20 mg of potash per gram of lubricant, of BN by the insoluble metallic salts of the overbased detergents, typically the metallic carbonates, the cylinder lubricant retains a good neutralizing capacity and good thermal resistance. Thus, the present invention makes it possible to formulate cylinder lubricants for marine engines, in particular for two-stroke marine engines, allowing them to be useable both with fuel oils with a high sulphur content and fuel oils with a low sulphur content and allowing them at the same time to have a high BN while maintaining the other performances of the lubricant.
Advantageously, the cylinder lubricants according to the invention have a good sulphuric acid neutralizing capacity. Advantageously, the cylinder lubricants according to the invention have a good thermal resistance. Advantageously, the cylinder lubricants according to the invention retain a good viscosity stability over time. Advantageously, the cylinder lubricants according to the invention present little or no risk of thickening as a function of the conditions of use.
In an embodiment, the cylinder lubricant according to the invention contains no fatty amines other than fatty amines corresponding to formula (I). Thus, the cylinder lubricant according to the invention can comprise one or more fatty amines of formula (I) but contains no fatty amines other than the fatty amine or amines of formula (I).
In an embodiment, the invention relates to a cylinder lubricant having a BN determined according to the standard ASTM D-2896 greater than or equal to 50 milligrams of potash per gram of lubricant, comprising:                at least one lubricant base oil,        at least one detergent based on alkali or alkaline-earth metals, overbased with metallic carbonate salts,        at least one neutral detergent,        at least one primary, secondary or tertiary fatty monoalcohol, the alkyl chain of which is linear or branched, saturated or unsaturated and comprising at least 12 carbon atoms, preferentially from 12 to 24 carbon atoms, more preferentially from 16 to 18 carbon atoms, advantageously the primary monoalcohols with a saturated, linear alkyl chain,        a mixture of fatty amines comprising at least one fatty amine of formula (I):R1—[NR2(CH2)3]3—NH2   (I)        in which:                    R1 represents a linear or branched, saturated or unsaturated alkyl group, comprising at least 14 carbon atoms,            R2 represents a hydrogen atom or a —(CH2)2OH group,                        the content by weight of fatty amine of formula (I) being greater than or equal to 90% with respect to the total weight of the mixture of fatty amines, the fatty amine having a BN determined according to the standard ASTM D-2896 ranging from 150 to 600 milligrams of potash per gram of amine, the percentage by mass of fatty amine with respect to the total weight of the lubricant being selected so that the BN provided by this compound represents a contribution of at least 10 milligrams of potash per gram of lubricant to the total BN of said cylinder lubricant and, the percentage by mass of overbased detergent with respect to the total weight of the lubricant being selected so that the BN provided by the metallic carbonate salts represents a contribution of at least 20 milligrams of potash per gram of lubricant to the total BN of said cylinder lubricant.        
In an embodiment, the cylinder lubricant essentially consists of:                at least one lubricant base oil,        at least one detergent based on alkali or alkaline-earth metals, overbased with metallic carbonate salts,        at least one neutral detergent,        a mixture of fatty amines comprising at least one fatty amine of formula (I):R1—[NR2(CH2)3]3—NH2   (I)        in which:                    R1 represents a linear or branched, saturated or unsaturated alkyl group, comprising at least 14 carbon atoms,            R2 represents a hydrogen atom or a —(CH2)2OH group,                        the content by weight of fatty amine of formula (I) being greater than or equal to 90% with respect to the total weight of the mixture of fatty amines, the fatty amine having a BN determined according to the standard ASTM D-2896 ranging from 150 to 600 milligrams of potash per gram of amine, the percentage by mass of fatty amine with respect to the total weight of the lubricant being selected so that the BN provided by this compound represents a contribution of at least 10 milligrams of potash per gram of lubricant to the total BN of said cylinder lubricant and, the percentage by mass of overbased detergent with respect to the total weight of the lubricant being selected so that the BN provided by the metallic carbonate salts represents a contribution of at least 20 milligrams of potash per gram of lubricant to the total BN of said cylinder lubricant.        
In an embodiment, the cylinder lubricant essentially consists of:                at least one lubricant base oil,        at least one detergent based on alkali or alkaline-earth metals, overbased with metallic carbonate salts,        at least one neutral detergent,        at least one primary, secondary or tertiary fatty monoalcohol, the alkyl chain of which is linear or branched, saturated or unsaturated and comprising at least 12 carbon atoms, preferentially from 12 to 24 carbon atoms, more preferentially from 16 to 18 carbon atoms, advantageously the primary monoalcohols with a saturated, linear alkyl chain,        a mixture of fatty amines comprising at least one fatty amine of formula (I):R1—[NR2(CH2)3]3—NH2   (I)        in which:                    R1 represents a linear or branched, saturated or unsaturated alkyl group, comprising at least 14 carbon atoms,            R2 represents a hydrogen atom or a —(CH2)2OH group,                        the content by weight of fatty amine of formula (I) being greater than or equal to 90% with respect to the total weight of the mixture of fatty amines, the fatty amine having a BN determined according to the standard ASTM D-2896 ranging from 150 to 600 milligrams of potash per gram of amine, the percentage by mass of fatty amine with respect to the total weight of the lubricant being selected so that the BN provided by this compound represents a contribution of at least 10 milligrams of potash per gram of lubricant to the total BN of said cylinder lubricant and, the percentage by mass of overbased detergent with respect to the total weight of the lubricant being selected so that the BN provided by the metallic carbonate salts represents a contribution of at least 20 milligrams of potash per gram of lubricant to the total BN of said cylinder lubricant.        
The invention also relates to the use of a cylinder lubricant as defined above for lubricating a two-stroke marine engine. The invention also relates to the use of a cylinder lubricant as defined above as a single cylinder lubricant that can be used both with fuel oils with a sulphur content of less than 1% by weight with respect to the total weight of the fuel oil, with fuel oils with a sulphur content ranging from 1 to 3.5% by weight with respect to the total weight of the fuel oil and with fuel oils with a sulphur content greater than 3.5% by weight with respect to the total weight of the fuel oil. The invention also relates to the use of a cylinder lubricant as defined above as a single cylinder lubricant that can be used both with fuel oils with a sulphur content of less than 1% by weight with respect to the total weight of the fuel oil, with fuel oils with a sulphur content ranging from 1 to 3.5% by weight with respect to the total weight of the fuel oil and with fuel oils with a sulphur content greater than 3.5% by weight with respect to the total weight of the fuel oil. In an embodiment, the cylinder lubricant as defined above is used as a single cylinder lubricant that can be used both with fuel oils with a sulphur content of less than 1% by weight with respect to the total weight of the fuel oil and with fuel oils with a sulphur content ranging from 1 to 3.5% by weight with respect to the total weight of the fuel oil. The invention also relates to the use of a cylinder lubricant as defined above in order to prevent corrosion and/or reduce the formation of insoluble metallic salt deposits in the two-stroke marine engines during the combustion of any type of fuel oil the sulphur content of which is less than 3.5% by weight with respect to the total weight of the fuel oil.
The invention also relates to an additive concentrate, for the preparation of cylinder lubricant having a BN determined according to the standard ASTM D-2896 greater than or equal to 50 milligrams of potash per gram of lubricant, said concentrate having a BN ranging from 100 to 400 mg of potash per gram of concentrate, and comprising at least one detergent based on alkali or alkaline-earth metals, overbased with metallic carbonate salts, at least one neutral detergent and at least one fatty amine having a BN ranging from 150 to 600 mg of potash/g of amine according to the standard ASTM D-2896 and of formula (I):R1—[NR2(CH2)3]3—NH2   (I)                in which:                    R1 represents a linear or branched, saturated or unsaturated alkyl group, comprising at least 14 carbon atoms,            R2 represents a hydrogen atom or a —(CH2)2OH group,                        the percentage by mass of said fatty amine in the concentrate being selected so as to provide said concentrate with a contribution of BN determined according to the standard ASTM D-2896 ranging from 20 to 300 milligrams of potash per gram of concentrate.        
The invention also relates to a method for lubricating a two-stroke marine engine comprising at least one step of bringing the engine into contact with a cylinder lubricant as defined above or obtained from the additive concentrate as described previously. The invention also relates to a method for preventing corrosion and/or reducing the formation of insoluble metallic salt deposits in two-stroke marine engines during the combustion of any type of fuel oil the sulphur content of which is less than 3.5% by weight with respect to the total weight of the fuel oil, comprising at least one step of bringing the engine into contact with a cylinder lubricant as defined above or obtained from the additive concentrate as described previously.